In American and Canadian football, a guard (G) is a player that lines up between the center and the tackles on the offensive line of a football team. The guard's job is to protect the quarterback from the oncoming defensive line and linebackers during pass plays, as well as creating openings (holes) for the running backs to head through. Guards perform speed blocking and "pulling"--sprinting out in front of a running back in order to block for him. Wikipedia
The definitive Wikipedia entry for Guard. Wikipedia is the biggest multilingual free-content encyclopedia on the Internet. en.wikipedia.org/wiki/Guard_%28American_football%29